A portal-type positioning device is described in European Patent No. 2 066 996; in this case, a transverse beam is supported in a mobile manner between two parallel linear guides, on which a functional element is movably held via a further linear guide, so that this functional element can be freely positioned in a plane between the two linear guides. For example, a gripper of a pick-and-place machine, a laser of a laser-machining center or also a probe system of a coordinate measuring machine are examples of functional elements. European Patent No. 2 066 996 focuses mainly on the most precise position measurement possible in such positioning devices, because precise positioning of the functional element is frequently of the utmost importance.
German Published Patent Application No. 10 2009 008 900 also relates to portal-type positioning devices of this type. For various reasons, they are not easily controllable from the standpoint of control engineering. Therefore, a device for controlling a positioning device is disclosed, which provides for especially precise positioning.
However, if the functional element which is guided on the transverse beam and positioned above the workpiece must exert considerable force on the workpiece, this may cause a deformation of the components of the positioning device. Because of the high leverages that are produced by the portal construction, even small deformations may result in a considerable displacement of the contact point of the tool on the workpiece, which is unacceptable for applications that make high demands on the positioning accuracy. One example of such an application is thermal compression bonding, in which electronic components are connected to a circuit board with the aid of pressure and heat. Forces of up to 500 N may be required for this purpose. On the other hand, positioning accuracies in the range of one micrometer and less required in such and similar applications are not unusual.
European Patent No. 2 783 791 describes routing the process forces acting on the tool not via the transverse beam of the portal-type positioning device, but by way of a separate force frame which is situated above the tool. The process force is thereby no longer applied by the portal-type positioning device, but by a pneumatic cylinder which is acting between the tool and the force frame. However, such pneumatic cylinders make it difficult to achieve a rapid switch between a high process force and pressure relief, as is advantageous for some applications, for instance thermal compression bonding.